text:
What is the purpose of the fuel pumps in the A320?
It might seem like a really stupid question, But i'm getting into flying the FBW A320 in MSFS2020 and I have no idea what the fuel pumps are for in the A320, please may someone explain and help a newbie out? Thanks

What purpose do you imagine they might serve? What research have you done on this question?

What do they do in your car?

It's not a stupid question, fuel pumps in a car have an obvious purpose, but airplanes have multiple fuel tanks and sometimes have pumps for cross-fueling and balancing weight.

Non-Airbus specific: You normally have an engine driven fuel pump (EDP) at the engines, supplemented by electric boost pumps in the wing tanks.  The engine driven pump provides direct pressure to the fuel control system on the engine itself, always well beyond what the engine needs, with excess fuel continuously returned to the tank, usually referred to as "motive flow".
The electric pumps in the wing tanks are to pressurize the lines to the EDP inlet so the EDP doesn't have to suck fuel all the way from the wing in critical situations, and they're also there as a backup to the EDP itself. You may also have electric pumps to handle fuel transfer and crossfeed functions.
The return "motive flow" from the EDP is also used to run ejector scavenge pumps, venturi pumps with no moving parts, like those plastic gadgets you hooked up to a garden hose to drain waterbeds back in the day. The scavenge pumps draw fuel from the tank extremities to a "collector tank" usually a well at the inboard end of the larger tank, open to the rest of the tank at the top and kept always overflowing by the scavenge pumps, and within which the electric boost pump will normally reside.

Your second paragraph seems to end in the middle

Missing period, and some finger trouble. Thanks.

Is it necessary to pressurize the fuel lines so that the fuel does not vapourize with the low pressure of the suction?

That's one benefit to having the boost pump running; resistance to vapour lock and you can have a minor leak in the plumbing between them and the EDP still gets its feed.  Some airplanes may run boost pumps all the time, some only in departure/arrival configuration or some such.


text:
What is the minimum runway surface friction coefficient?
After calculating the friction coefficient for an asphalt runway pavement through a test, how to know if it’s acceptable or not? In other words, hat is the lowest acceptable value for friction coefficient specified by ICAO or other related organizations?

Do you mean for dry pavement? Or the lowest that aircraft can operate on?

The lowest acceptable for dry pavement

Depends on speed.

ICAO
In Doc 9137, Airport Services Manual - Part II Pavement Surface Conditions, ICAO requires 3 levels of friction to be defined at local AIP level.

3.2.11 States should specify three friction levels as follows:
a) a design level which establishes the minimum friction level for a
newly constructed or resurfaced runway surface;
b) a maintenance friction level below which corrective maintenance
action should be considered; and
c) a minimum friction level below which the information that a runway
may be slippery when wet should be made available and corrective
action initiated.

They also provide a sample table:

which is based on experience with different friction-measuring
devices, shows the criteria in use in some States for specifying the
friction characteristics of new or resurfaced runway surfaces, for
establishing maintenance planning levels and for setting minimum
friction levels.

Actual values for the US are therefore defined by FAA:
FAA
In AC 150/5320-12C, levels are defined according to the measurement method, with the three levels recommended by ICAO. At first sight there is no difference with ICAO sample table.

TABLE 3-2.  FRICTION LEVEL CLASSIFICATION FOR RUNWAY PAVEMENT SURFACES

UK CAA
A similar table is found in CAP 683:

EASA
Apparently there is no EASA equivalent, each State member of EASA seems to have it own method. For more information, see this study to try move forward, without apparent further actions.
On the other hand the friction matter is a complex one, and measuring the state of the runway under some conditions does not give all the information required to evaluate, say the length required in case of RTO or for braking in rainy weather.

Related: How are runway conditions measured?

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text:
Does anyone know why IAS and Mach are inconsistent in Boeing FCOM?
The following figure is extracted from Boeing FCOM that I downloaded from the Internet:

I noticed that Mach and KIAS values are inconsistent. An example is in red box. Let me show what I found:
$$ \text{IAS} = \sqrt{\sigma} \times \text{TAS} = \sqrt{\sigma} M a $$
For ISA @35,000 ft: $ \text{IAS} = \sqrt{0.3099} \times 0.797 \times 576.4 = 256 \text{kts} $
Speed of Mach 0.797 is calculated to be 256 KIAS but the red box shows 271 KIAS. Does anyone know why IAS and Mach are inconsistent?

What you calculated is Equivalent Airspeed (EAS), not Indicated Airspeed (IAS) or Calibrated Airspeed (CAS). The formulas to calculate these speeds from the True Airspeed (TAS $ = Ma $) are:
$$ \text{EAS} = \text{TAS} \sqrt{\sigma} = M a \sqrt{\sigma} $$
$$ \text{CAS} \approx \text{EAS} \left( 1 + \frac{1}{8} (1 - \delta) M^2 \right) $$
(formulas from Wikipedia, valid below Mach 0.85)
Here, $a$ is the speed of sound, $ \sigma = \rho / \rho_0 $ is the density ratio and $ \delta = P / P_0 $ is the pressure ratio. You can find the values for ISA e.g. in the table in this answer. At FL350, they are $ a \approx 573 \, \text{kt} $, $ \sigma \approx 0.3099 $ and $ \delta \approx 0.2353 $.
Plugging in the given Mach number of 0.797 then gives:
$$ \text{EAS} \approx 254 \, \text{kt} \qquad \text{and} \qquad \text{CAS} \approx 270 \, \text{kt} $$
The difference between CAS and IAS is usually small (only a few knots). It is possible that Boeing took that into account in the table, or they use the terms interchangeably and my result of 270kt is just a rounding error.

The speeds in Boeing's table are consistent.
To demonstrate that, we will have to know how to convert between Mach and CAS. There is no need to convert to true airspeed, the relation between CAS and Mach is well defined.
Calibrated airspeed is purely based on impact pressure, which can be measured by a pitot-tube.
For subsonic speeds:
$V_{CAS}=a_{0}\sqrt{5\left[\left(\frac{q_c}{P_{0}}+1\right)^\frac{2}{7}-1\right]}$

$V_{CAS}$ is calibrated airspeed
$a_{0}$ is the speed of sound under standard sea level conditions (340.3 m/s)
$P_0$ is the static air pressure under standard sea level conditions (101325 Pa)
${q_c}$ is the impact pressure

The impact pressure for compressible flow is:
$\;q_c = P\left[\left(1+0.2 M^2 \right)^\tfrac{7}{2}-1\right]$

$P$ the static pressure
$M$ the Mach number

In standard atmospheric conditions at FL350:

the pressure is 23842 Pa.
the temperature -54.35° C or 218.8 K.

Filling in the numbers gives:
$\;q_c = 23842\left[\left(1+0.2\cdot 0.797^2 \right)^\tfrac{7}{2}-1\right] = 12393.4  $Pa
$V_{CAS}=340.297\sqrt{5\left[\left(\frac{12393.38}{101325}+1\right)^\frac{2}{7}-1\right]} = 139.3 \textrm{m/s} = 270.8 \textrm{KCAS}$
Close enough!

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text:
What flap design does the A380 use? Is it Fowler flaps, slotted flaps or a combination?
I have looked at maintenance manuals, the Airbus website, and Wikipedia but still could not find a definite answer as to what trailing edge flaps the Airbus A380 uses.

Airbus calls them single slotted, tracked high lift flaps in this presentation:

When watching the flap extension in this YouTube video you can see that the flaps extend backwards and downwards at the same time, which would make them single slotted Fowler flaps:


text:
Where are the "Admitted Aircraft symbols" on Jeppesen VFR aerodrome charts defined?
Jeppesen VFR aerodrome charts depict several symbols for "admitted aircraft". However, even after checking several symbol legends I never found a definition of these symbols. Does anyone know where these are defined?

Are you asking what the term "admitted aircraft" means, or what each of the various specific aircraft symbols mean, or both?

@quietflyer I'm looking for a definition of the symbols, meaning which aircraft are admitted. The third one seems to be a glider and the last one obviously a helicopter, but what do the other symbols mean?

4th is probably ultralight, but what on earth is difference between 1st and 2nd?

Tricycle gear vs. taildragger maybe?

@quietflyer The first symbol admits aircraft that have lost their propeller and are now gliders.  The second admits those that still have their propeller.

1,3,4 & 5 are pretty obvious. 2 is the baffling one IMO

Really, the 2nd is evocative of a warbird, but that wouldn't make any sense.

I was actually thinking warbird for 2 but am trying to find a definitive answer

With the help of Bianfable's answer I took it upon myself to email Jeppesen to get the correct answer.

Excellent, thanks for going the extra mile.

These symbols are part of the Jeppesen VFR Manual (formerly called Bottlang Airfield Manual). The Jeppeson website contains a sample for one airfield:

(3) Aircraft admitted at the Aerodrome / Am Flugplatz zugelassene
Luftfahrzeuge

Unfortunately, the sample does not explain what each of the aircraft symbols mean. A briefing bulletin announced some change in the design of these charts, but also does not explain the symbols:

Unlike the IFR charts legend, Jeppesen does not publish a legend for the VFR Manual online. So it looks like you have to purchase the full VFR Manual (either from Jeppesen or other dealers, price is over 100 euros).
If you search on Google, you will find some (probably illegal) uploads of VFR Manuals on several dubious websites. I'm not going to download any of those, but if you really want to know, you might find an answer there.

Thank you for your answer. I would’ve accepted it and given you the bounty if nobody would’ve posted the definition. However, as wbeard52 even contacted their support and has posted a definition, I accepted his answer.

@rauberdaniel I fully agree. Especially considering my answer says you have to spend hundreds of euros and wbeard52 got it for free, I think he deserves the bounty :)


text:
Is engine damage due to a fan blade failure irreparable?
I have a question related to this question and this video. The question says that sometimes a fan blade failure can occur.

My question now is, if a fan blade separates or a malfunction occurs, is the engine still repairable?
I think the damage to the engine's structure would be quite high?
According to the video a fan blade malfunction occurred on start-up, how could a malfunction appear on start-up?

This depends on the failure: A fan blade can be damaged by birds, debris, or aircraft parts (pitot probe for example).  In this case the blades are dented, in which case it is possible to replace the damaged parts, inspect the engine and re-use it.
For this kind of damage it has to be disassembled and inspected by the engine manufacturer.
Inspection of blades is done with a microscope: For example, I have seen an HPT blade declared unserviceable because of a small scratch.
Obviously if the repair costs more than a new engine you don't repair the old one.
Many more things can happen in startup:

The engine is run on full power
There is a lot of possible interactions (like birds for example) that you don't have in a steady cruise at 40,000 feet.

Aside from debris, you can also have a compressor stall like this.

remember reading about an early F/A-18 test flight where they had a bird strike, animal damaged the front fan, several blades went right through the engine (together with deep fried bird parts) and out the other end. Apart from the initial bang and the engine running a bit hot and losing partial power the pilot noticed little.

I think it depend of the engine itself, military engine are very strong engines. See what can be happen in commercial engine : https://www.youtube.com/watch?v=ji4nZ5k82uk

of course it does. And on what hits it, what breaks, etc. etc. And a pretty solid dose of luck...

Your link to "a compressor stall like this." broke

Jet engines are fairly expensive, accounting for a large part of the cost of an airliner. So there will be some incentive to repair the engine if possible.
Whether an engine is repairable is dependent on the failure. If it happens at startup and mostly causes a bunch of smoke, like in the linked video, then the damage may be fairly limited and will probably be repaired. If damage is suspected, a borescope inspection is generally done to check the inner parts of the engine for damage as well. If a failure happens at full thrust, the engine is probably finished. Aircraft and engines are designed for this failure, but a full blade failure will cause extensive damage. Parts that get loose and enter the engine core will cause further damage through the engine.
Also, serious failures are generally investigated, especially if they are considered uncontained. This will mean at least extensive downtime for the engine, and may or may not end up being repaired.
There are many malfunctions that can occur at startup. The engine has been shut down for some period of time, during which:

Parts cool down and contract
Debris can enter the engine
Things can leak or get damaged

Whatever has changed will be discovered when the engine is started. Also, the problem in the video seemed to only appear after taxiing for some distance, so the engine could have ingested FOD at some point. It's not clear whether the 10 minute hold is due to ATC or the pilots noticing abnormal engine parameters.

Depending on the jet engine type and on the cause and amount of damage, an engine repair or module replacement could be carried out on the wing. If damage or further investigation is needed, or if the aircraft is needed quickly, the engine could be removed to the airline's engine shop and parts/module/modules replaced on site.
Further damage may dictate the engine goes back to the manufacturer's overhaul shop or an approved overhaul facility: The engine will be stripped and each part inspected for serviceability. The cost of repair will be calculated. If the repair cost is higher than a new engine cost, the insurance company may deem it "beyond economical repair" and the engine is scrapped.
If the repair cost is acceptable then the engine may be repaired or fully overhauled depending on the operating hours/cycles already accrued in service: A low-hour damaged engine may just be repaired, whilst it would be more economical to fully overhaul a high-hour damaged engine to bring it back to "nil hours since last overhaul status".

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text:
What stops planes from being stolen?
Related question: do planes have keys?
Let's say I happen to spot a fine-looking plane at my local airport and decide the owner probably wouldn't mind if I borrowed her for a little while - what stops me from stealing this plane? On commercial jets, the cockpit door is locked, but as I understand smaller planes don't have cockpit doors. The linked question suggests that single-engine planes have ignition keys, but twin-engine planes don't. Are the outer doors (cabin doors) locked? What else restricts me from walking up, climbing in, and flying away? (Other than the fact that I don't have the least clue how to fly a plane.)
(This is about all types of planes.)

The barriers to theft are typically access to the plane and knowledge of how to operate it.

Laws and jail time are effective in preventing theft

@SteveKuo they may be somewhat effective, but car theft is still a somewhat serious issue, and that's illegal too (at least in the US)

Very Little

@raptortech97 - With the introduction of the Immobilizer system into most newer cars, theft of the car itself is on a rapid decline (though smash and grabs and in-place strip-downs like wheel thefts are still common). The main problem with putting them into most civilian aircraft is that they'd be too easily bypassed because of the simplicity of the rest of the engine system. It works in cars because those engines are computer-controlled and won't even idle properly if the computer's not working. on an aircraft it would basically control the magnetos switch, and you can bridge that in seconds.

There are a several theft-deterrent mechanisms in place.

On small airplanes, most commonly, the door to the airplane itself is usually
locked with a key. (Notice the key cylinder in this picture below the silver door handle:
Prop locks:
Throttle locks:
A lot of airplanes do have an ignition key which you turn to engage the starter.  Of course, as jaytre mentioned, this can be circumvented by hand-propping (which is a very dangerous endeavor for unskilled people who haven't done it before)
You would have to know how to operate the basic systems of the airplane as well as how to fly.
AOPA's Airport Watch Program
Fences and other physical security measures around airports.

C172s have the magnetos controlled by a key too, so you can't hand-prop it unless you hotwire it first (the same key that's used to operate the starter and to unlock the door)

Is that prop lock just a chain wrapped around the prop? Seems like someone with a spanner could take off the prop and then remove the chain and reattach the prop.

@ratchetfreak Taking off the prop is a much more complicated endeavor than that. The prop is a carefully balanced instrument!

Personal anecdote time: my father used a prop lock on his Cessna. The thieves specifically wanted the propeller. They left the lock behind...

Hand propping wouldn't get you past the magneto keyswitch, but unscrewing the ground terminal it connects to would render it useless. (In some planes you wouldn't even need to hand-prop it because the starter is activated by a button…)

@ratchetfreak That would involve the thieves spending a very large  amount of time working on the plane, risking somebody seeing them.

Perhaps an added wrinkle: when I worked ground crew at flight school, more often than not I could get into one of the schools C172R's with a key that belonged to a different 172.  I've heard a similar tale from some flight students who lost their keys on after landing out at a different airport and borrowed keys from the FBO's 172 to fly home on.  Is there anything being done to address this, or is that where the throttle locks, prop locks, etc. come in?

@Marius I think if you look at JanHudec's answer about legalizing a stolen aircraft helps to deter that as well. But yeah, if you were super concerned about your plane being stolen by someone trying out a key from a similar airplane, then prop/throttle locks are the way to go.  Additionally, it is a Federal Office with pretty hefty penalties for stealing aircraft. A lot more than say, stealing a car. [citation needed]

Does that proplock actually lock the propeller to anything?

@Sean no, it's just makes it so that the propeller can't move.

@Canuk: How does it make it so the propeller can't move if it doesn't lock the propeller to anything else?

@Sean it’s a heavy think chain that is too small to be slipped off by sliding it over one blade. Technically the propeller could move, but it’s not going to be able to turn on the engine without destroying the airplane.

The difficulty of first hiding and then legalizing the aircraft.
So the thief got into the plane. But what's he going to do with it? A car can be repainted in any remote garage and nobody will notice and registration is just a piece of paper relatively easy to fake. But aircraft can't be landed just anywhere. So police has manageable list of places to check for the plane and by looking at ATC recordings they can help further narrow down the search. Even if the plane flies through uncontrolled airspace only it may come up on primary radar now and then. Or get noticed by some witnesses if it flew very low to avoid that.
And then the thieves need to get a new registration for it to be able to use it or sell it. So they have to create a fake registration and re-register the plane. But for planes this is much more thorough process than for cars, so the risk the civil aviation authority of given state will notice some discrepancy between the fake papers and various databases that will inevitably exist is again pretty high.
So even if the thief would be able to get into the plane, they would have hard time avoiding being caught later, taking away the motivation to try stealing a plane in the first place.

tl;dr fencing a stolen aircraft is a lot more trouble than fencing a stolen car

+1 They have records of nearly every airframe ever built, at least by any significant manufacturer. If you use a fake serial number, they'll know it's fake. If you use a real one, they'll know who it belongs to.

I guess one might steal a plane for just flying one for fun. And what drug lord operating a landing strip in the jungle cares if their planes are not properly registered?

@sanchises: Actually, any sane drug lord does. He needs the planes to take the stuff from the jungle to somewhere they can sell it and the later point likely has air traffic control coverage and towered airport. Any doubt about aircraft registration could just draw undesired attention to the other part of the operation.

@JanHudec Fair enough, I guess I'm not really cut out for drugdealership.  Such a missed opportunity.

@sanchises And as far as taking a small plane for a joyride, the result is usually tragic. Even if you survive, because a plane is a motor vehicle under most state laws (though obviously registration/inspection/taxation are much different), stealing a plane is felony grand theft auto.

@KeithS: Isn't stealing any motor vehicle felony grand theft auto?

@Vikki I think that was Keith's point. "Because a plane is a motor vehicle,... stealing a plane is felony grand theft auto."

Don't know about larger jets, but GA planes do have keys, which enables the engine to cycle by ungrounding the circuit that allows a charge to pass from the magnetos to the spark plug. That said, they are usually very low-tech. I don't think engine compartments are ever locked and you could do a small bit of rewiring to bypass the ignition switch pretty easily then hand-crank the prop to start it.
To combat the low-tech ignition, many planes have lojack installed & are kept in locked hangars. Also, most airports have security cameras and ATC records radar, so a stolen plane would be pretty easy to track down.

Thanks! To clarify, it also sounds like the cabin doors don't have locks?

Often cabin doors do have locks. Some cockpits aren't fully enclosed, so those obviously wouldn't need them.

I'm not sure that lojack for aircraft is particularly common - I don't think I've ever seen an aircraft with it installed...

+1 for locked hangars, seems the most common/important measure in my area at least.

How many small GA owners afford hanger space, vs tie down.

You mis-understand how magnetos work.  They are specifically designed to need no external power at all - to produce a spark, all you do is rotate them (by rotating the engine).  The "ignition" key on a small plane grounds the magneto to the airframe when the key is in the "off" position to PREVENT them from producing spark.

@SkipMiller - The point I was attempting to make was that without a key you'd need to rewire the magnetos to bypass the ignition switch for them to operate. By sending power, I meant completing the circuit. I've updated the answer. Thanks

@jaytre: Again, not quite right.  The key in the "on" or "start" position does not complete the circuit - it breaks the so-called "P-lead" circuit so that the mag is no longer grounded and the electric power surge can reach the spark plugs. What you describe as "re-wiring the magneto to bypass the ignition switch" is more simply described as "disconnecting (or cutting) the P-lead".

@SkipMiller - I see what you're saying & that's certainly news to me. Thanks for clarifying. Answer updated

I think rewiring is the wrong word to use to bypass the ignition switch, "cutting wires" is more exact

There are a few factors that come into play. I will try and provide what they have and how to get around them.

Locked airport...

Most airports I have been to have some form of a fence, gate etc so you would need to get past that first. Chances are there are also cameras but a ski mask and gloves will help you out with that. Smaller fields may have less protection and you may even be able to walk right up to the hangar. But you may draw more attention to your self as the people at the smaller fields may know each other better and know that its not your plane.

Locking the plane up...

Some GA planes are hangared in presumably locked hangars. So the first thing you would need to do is get into the hangar. In this case we are talking about a door lock or a pad lock of sorts which can be generally opened with this if you practice a bit.

Ok now you are in the hangar/have the hangar door open...

Most General aviation planes do have door locks form what I have seen. These locks tend to be of the smaller key type (think pad lock key size) but Im sure they vary and newer planes carry larger keys. Most of the locks I have seen can be picked with something like this. There are types of locks that are better at preventing picks (like tubular) but they too can be picked.

Ok now you are in the plane...

Maybe the plane has a prop lock (you can get that off with a bolt cutter, but don't nick the prop).
Maybe the plane has a throttle lock, back to our lock picker to get that off.
Now you need to start the plane up. Here you have a few options one of which is to use the lock picker to turn the ignition key. Personally I would not do this for simple flight safety reasons. In this case you would bring along 3 switches with wires hanging off of them (this would work better on older planes) get under the panel and splice in some bypass switches. This would allow you to control each mag and the starter. You could also try a simple flat head screw driver and some good old force to break the tumbler and operate the starter. On newer planes with sleeker one piece dashes you may have an issue getting being it to hot wire it but I would think there is a way.

Ok now the engine is started....

The plane is running and you are taxing out, assuming no one in a nearby hangar asked you what you were doing and where Bob (our fictitious victim) was and why you were flying Bobs planes. No one is going to stop you on the taxi way or from the tower as far as I know. Now you are in the air, flying VFR to somewhere. Lets say Bob still has no idea his plane is missing since he does not intend to use it all week. You get to your home base airport with the plane and still no one is wise to what you have done. Maybe its even a private strip and no one else is there to say anything.

Now you have the plane in a "safe" place....

The first thing you do is get the plane out of sight, put it in a barn maybe, get out your aircraft paint stripper and get rid of that N-Number would be your first task. Maybe strip more of the paint so as to make the plane harder to identify. Now you are thinking you will do one of two things with the plane, use it your self or sell it.

But you need an N-Number...

The first thing you will need to do is get a new N-Number for the plane this is where you will hit a problem as the airframe is already registered to Bob so you can't use that airframe number. I am under the impression that this where the road will end for you as its harder to fake an airplane number since they are far more closely tracked than say a car vin where you can use one out of a wrecked car (to an extent, its still illegal but technically can be done) There may be salvation laws for planes as well that you can exploit here if you can get a wrecked version of the same plane.

But Can I Sell It...

Maybe you can part it out and sell it, plane parts do command a high price. But with out the log books you may have an issue proving the time on a lot of the parts. Chances are Bob did not leave his aircraft logs in the plane but maybe he did (bad idea Bob). Now you can just part it out but you cant sell the whole plane. In trying to do that someone is going to be asking about the lack of N-Number and the log books. But hey, you tried.

What about a joy ride...

Well sure, we have already established that you can get into the plane and fly it away, you could very well return it (with a bunch of broken locks) to where you found it.

The only question is can you fly the plane...

Remember every plane is different, while you may be able to saunter into the cockpit of some pretty heavy metal you may have no idea what you are doing or how to get it off the ground. I have no idea how to start a jet engine so I doubt I could just hop in one and fly away no matter how accessible the plane is. Lets say you have used X-Plane a bit to much and know how to start up and (theoretically) fly the plane, everyone here knows that theory and practice are not the same thing. Even if I got into the cockpit of a running jet I would still need to actually fly it. So on some level you are limited by experience unless you are a well trained pilot, well trained thief, and in general a criminal.
Please note I do not condone or endorse (or have ever been involved in) aircraft theft in any way. For the sake of argument I am presenting the facts to answer a hypothetical question. If for any thing, don't ruin Bob's week....

If you're already doing something illegal, what stops you from simply flying the plane without a registration number?

@Sean I would assume that the local air force would be interested in a registrationless aircraft out there.

Given the very lightweight construction of GA aircraft, any physical security to the cabin will do nothing more than make the owner feel better about it. Propeller locks like the one in the other answer's picture are highly effective - you won't be going anywhere with it on, and it makes an awful lot of noise cutting it off. mind you don't cut the prop blade in the process.
Commercial jet cockpits aren't locked to prevent someone flying away with it, they are locked to prevent hijacking. This is new since 2001 - before that the cockpit door was no stronger than the one on the toilet.

The physical security will do something. It will differentiate thief from authorized person on the security surveillance camera footage.

True, assuming the GA airport has cameras.

Even if it does not it increases the risk somebody will notice and call the police.

Cockpit doors have been locked since 1964, not 2001 (although the reasons are essentially the same as given in the answer).

Nobody so far seems to have mentioned gust locks. These are physical blocking devices intended to prevent the movement of control surfaces. Some are placed directly on those control surfaces, others are placed in the cockpit on the control column.

The primary purpose of most such devices is not a theft-deterrent; they're typically used to prevent the control surfaces moving incidentally while the aircraft is parked (mainly due to high winds, hence "gust" lock), but some designs can be keyed to prevent their removal by someone other than a keyholder (again the primary intention is not theft prevention, but more a "maintenance lockout" preventing manipulation of control surfaces from the cockpit while a mechanic is working with moving parts), and such devices would be the equivalent of "The Club" for aircraft, preventing a would-be thief from being able to maneuver the aircraft even on the ground.
Some locks are intended to stymie operation of the aircraft in any meaningful way with the lock installed (for instance, physically blocking access to the magnetos switch), but nothing's foolproof (fools are too inventive) and there have been several fatal crashes recorded where the pilot attempted to take off with a gust lock still installed and the resulting loss of control was unrecoverable.

"there have been several fatal crashes recorded where the pilot attempted to take off with a gust lock still installed and the resulting loss of control was unrecoverable." Seems like the solution would be to design the lock in a way that impedes some action necessary for takeoff?

Just to see how "easy" it is you can watch here:
http://www.discovery.com/tv-shows/airplane-repo/
Even though they have a skilled pilot, fun television crew for distraction and staying low key, permission slip to reposess, etc.. it's still no easy feat to actually pull off as the show proves.
The other answers already point out the problems you encounter when actually trying this and having the airplane :-) but I'd thought i'd point out this show.

Two important things here: Presence of a very skilled pilot with experience in many different airframes, and almost more importantly: a plan for what to do with the plane once they have it in their possession (return it to the lender).  I'm sure you know but worth pointing out: the TV crew wasn't actually there when it happened for real. It's all re-enacted (poorly and hilariously).

One person who had their airplane “repossessed” on that show said the producer paid him (the ex-owner) to play the part of the repo pilot in his own plane, and then he flew it to the location requested by the bank. It is a complete fabrication from start to finish.

Well, theoretically nothing.
As mentioned above, there are some security measures such as secure airports with secure access ramps, security personnel around the clock, ramp lighting with periodic visits from airport police.  Aircraft can be kept in locked hangars equipped with alarms and video surveillance.  And the entrances to most aircraft can be locked.
Then there's the aircraft itself.  Most small GA aircraft have key imterlocks on their starters.  Owners have become pretty complacent and have left keys available in the aircraft, which facilitate the theft spree in 2010 by Colton Harris Moore aka The Barefoot Bandit.  Moore used these opportunity combined with a little piloting experience gleaned from Microsoft Flight Simulator to steal several GA aircraft, including one from Indiana all the way down to the Bahamas.

Larger, more complex aircraft do not.  However they generally have specific startup procedures or may require external sources of electric or pneumatic power to start up, not commomly known to a typical thief, making it difficult st start up, as a guy who tired to steal a life flight helicopter recently found out.

Your video link breaketh.

There is a threat that a large heavy jet could be stolen while parked at a remote airport at night (see Skywest aircraft stolen video). The crew entry doors and cockpit doors are not locked when not in flight. There are other means of entering the aircraft through electrical doors or cargo door area.
 You do not need keys to start the aircraft and everything from starting the APU to the engines is done by toggle or push button switches. Airport security is the only protection and the fence line.
  Its just a matter of time before its done and flown into the closest large living structure after takeoff. 9-2-2014 10 Airbus aircraft stolen from Libya, 5-25-2003 727 stolen all these aircraft are still missing.

do you have sources for the last statements you make?

The Libyan situation in 2014 is hardly relevant since the rebels captured the whole airport.  This was part of looting during a war, not just a thief who slipped off with a few planes.

This is for Federico Google the Libya aircraft stolen A300 aircraft. The 727 has a long history and searched for by the FBI,CIA and TSA.
This is for Cody P: You are correct in regard to the Libyan situation. The point is that it can be done in the US also. How do you get 10 A300's flown out of a Libya by a bunch of rebels.
I have been a pilot and heavy jet mechanic for 42 years for a major freight airline. Its not if but when this will happen. I invented a tool to prevent it have a patent pending but no customers because the FAA,TSA have not mandated it. Just a matter of time! You can steal a general aviation aircraft very easily if you know how to bypass the Mag system without the key. But as a weapon you can not do much damage. As for heavy jets we all saw what happened on 9-11!

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


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How is fuel dumping safe?
The answers to this this question make it clear how modern airliners dump fuel in the case of an emergency. As far as I understand, fuel dumping might be done to lower an aircraft's weight to the maximum landing weight, particularly soon after takeoff.
As far as I understand, jet fuel is typically not safe. When I, as a complete outsider, hear of fuel dumping, I imagine a whole bunch of dangerous corrosive fuel being dropped on whatever happens to be below, and it sounds like a frankly awful idea.
What makes fuel dumping safe, or if it is dangerous what makes it worth it?

Jet fuel isn't corrosive and the dumped fuel evaporates before it reaches the ground anyway.

Lol at "dangerous corrosive" fuel. It's kerosene, sprayed over a very big area.

@DavidRicherby: That depends on many conditions like rain, temperature and altitude of dumping. I can remember a situation where some test airbus dumped fuel over our living area and you could smell it.

Here's some aircraft maintenance trivia: we called the valve that controls the dump a Jesus Valve. I'm not sure what the pilots call it, but its a bad day if they have to use it.

At that height even if you blow a nuke nothing will be felt on the ground except EMP.

Fuel dumping is almost always an emergency maneuver, and it is never good for the environment.  So the alleged danger from the dumping must be balanced with the imminent danger to the 200–400 passengers involved.  It is never an easy decision but that's why the Captain gets paid the big bucks...
Dumping fuel sounds dangerous but it is not.  It is not going to explode.  Jet-A can be compared to kerosene and I don't have that statistic so let's compare it to Diesel Fuel which is not dissimilar to Jet-A.  Diesel Fuel at 400°F(204°C) is as volatile as gasoline is at 70°F(21°C).  Obviously that is a big difference.  Jet-A also evaporates into the air, so little if any hits the ground.
The biggest danger I see is to the atmosphere.

misted fuel can still ignite but if you are going at mach 0.7 it won't catch up to you

Since when do airline pilots get paid the big bucks? ...or is that a joke? :)

@egid - The starting salary for a captain with a medium-sized airline may range from £57,000 to £78,000, while those with the major operators could earn from £97,000 to more than £140,000. A pilot's salary is often incremental, rising with each year of service with the company. Sure, it's not millions, but that is pretty big amount of money.

@egid: Yes, meant to be a joke.

@Davor those numbers seem pretty high for US carriers. Maybe it's different overseas.

@Davor See Do commercial airline pilots make around $19,000 - $25,000 per year?

@DJClayworth - so? A pilot with zero experience flying bananas from Brazil makes 20k. Terrible. Or do you expect every newbie to make as much money as renowned experts in the field?

@egid - I worked for Delta Airlines in aircraft maintenance in the 1990s. I saw a wide body pilot's paystub (wide body is significant because more senior pilots fly it). The pay stub was left in the cockpit during an overhaul. I don't recall how much the captain made. But I made about 50K or 60K a year, and I recall the captain put that much in his 401K that year. I don't think anyone makes that kind of money anymore (except the executives, whose pay probably went up while others were taking pay cuts).

@DJClayworth: It seems to be situation specific to the US where many private pilots want the job. In parts of the world without that big pool of private pilots the wages are better.

I beg to differ about the decision to dump fuel being difficult. Nope. If you face a situation where you must land sooner than expected and you're over max landing weight, you dump fuel if your plane has that ability. As simple as that. There's no telenovela style gazing in the cockpit, no extra perspiration, no echoing voices pondering all the mistakes you made in life. Just find an apropriate area nearby, dump whatever you don't need and land. It damn sure is not on the list of things that justify higher than average wages of airline pilots.

It's not really safe in an environmental sense, but it's not that bad.  Jet fuel is essentially kerosene, which is harmful, but as far as engine/industrial fluids go, it's pretty benign.  Additionally, when an airplane dumps it, it's diluted so much by the time it makes it anywhere that it's not a significant concern anymore.
On the flip side, if an airplane didn't dump fuel and landed overweight, the potential side effects could be disastrous and could result in many injuries and damages.
Basically, it's choosing between two bad options, landing overweight or dumping fuel, and dumping fuel is the least bad of the two of them.
In any case, it's quite a rare occurrence.  You are exposed to far more toxins just walking down the street of a city than from airplanes dumping fuel.

Great answer but I'd like to add that the cost of dumped fuel is another consideration, which you have to sacrifice for safety.

Up-voting @skipmiller, I offer this addendum

if it is dangerous what makes it worth it?

Emergency Landing After Takeoff
Large aircraft typically cannot land as heavily as they can take off. It's a structural issue. So fuel dumping would be done if an emergency did not allow the time to burn down to allowable landing weight.
Maintain Flight with Engine/Power Loss
If available power did not allow sustained flight one might dump fuel. Worse if you were over mountains and needed to stay high.
Ditching
There was a case of a C-130 - a high wing plane - ditching in the Atlantic. It floated for a couple days with empty gas tanks and had to be shelled to force it to sink.
Fuel Leak
If a wing tank fuel leak was causing aircraft balance problems one might dump from the opposite wing to keep the aircraft controllable.
Life Imitating Fiction
15 minutes after takeoff we lost all thrust on 3 engines. Our gross weight forced us into a controlled descent. Dumping most of our fuel might very well have kept us airborne on 1 engine, if not I think empty tanks would have limited possible fuel fire in the controlled crash. I was about to dump 45,000 lbs of JP-4 all over west Texas when we solved our engine problem.

Very cool points, but I don't understand the ditching example. Was fuel dumped to make the plane lighter so it would float better?

Navigation error caused them to run out of fuel.

So what does it have to do with fuel dumping? Have there been any cases where a plane has dumped fuel specifically to float better after ditching?

It's a consideration. And I just illustrated the point where empty tanks helped keep the aircraft afloat. But I may concede a point - I don't think Sullenburger dumped fuel when he went into the Hudson. I don't think his airplane had a dump system.

Just to point out that while an empty tank will certainly float better than a tank full of Jet-A, the full tank will also float because Jet-A is around 6.7 lbs/gal and sea water is greater than 8 lbs/gal.

@Terry only if the Jet-A + the steel/aluminum container and whatever is attached to it is lighter than water, it's not enough that the Jet-A is :)

 I was about to dump 45,000 lbs Well, better safe than sorry, wouldn't it be better to dump it anyway in case they fail again ?

Fuel dumping is done by many types of Aircraft(fighter etc.) it is not limited to the role(cargo, passenger etc.). Although the purpose may be same.(Sometimes its done to reduce the load, to avoid any accident).
In a fighter plane fuel is dumped to reduce the weight and increase the distance to cover(the weapons it carries already has tons of weight on the plane). This could be the same in passenger but situations may vary.
Fuel dumping is really a serious threat to the environment or the biological impact  especially if it's dumped in the water(causes damage to maritime species and irreversible damage to the coral reefs if present).

I'm gonna go ahead and say dumping fuel from a fighter plane won't increase its range.

Not range but payload/speed


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Could landing gear weighing scales be used to detect lack of lift?
There have been several crashes due to ice on wings destroying lift. One of the issues with this is that you can't detect that you don't have sufficient lift until you're already in the air, way too late to abort.
Some aircraft have weighing scales in the landing gear. Could these be used to verify the expected lift, and abort if an anomaly was detected before $V_1$?

significant lift doesn't happen before rotation at $V_r$ which is after $V_1$ and
The pilot would have no time to look at those, he is focusing on keeping the plane centered on the runway and pressing the brakes.

@ratchetfreak the linked question definitely answers in terms of calculating weight and balance, but doesn't consider the possibility of verifying the lift curve. And I might be wrong, but I believe if normally get 30% of weight in lift just prior to Vr, a contaminated wing would give significantly less, perhaps 20%, and this anomaly could be detected automatically.

@raptortech97 Just before Vr, you're still after V1. Past V1, there's not a whole lot you can do if the plane's not flying.

Sorry, I meant just past V1. The idea is that the wing should be generating some small amount of lift. If that amount of lift is significantly less than expected, we can abort the takeoff.

just past $V_1$ is still after $V_1$ and after the point of no return.

@ratchetfreak agh, sorry, I meant before V1

I don't really agree with marking as duplicate. The other question is about whether aircraft have scales or not, whereas this question talks about the usage of these scales. Related? Yes. Duplicate? I think not.

@ROIMaison I made a very major edit after it was marked as duplicate that, in my opinion, made it no longer a duplicate. If you look at the edit history, though, the original question was close to a duplicate

Ah ok, shouldn't someone (who is able to) remove the 'marked as duplicate'?

@cpast: If the plane's not flying, you're going to have to abort, after V1 or no.

Technically one could develop a system that compares the decrease in weight-on-wheels during the take-off run to a theoretical lift model in order to determine whether the wings are performing as expected.
I see a number of reasons why this will not be successful a product:

Limited benefits:
The benefit of such a system is minimal. There are very few crashes due to contaminated wings or wrong flap/slat configurations. Let's assume there are one hundred thousand airline flights per day and one lift related take-off crash every 4 years. That is one in 150 million.
Available alternatives.
For both causes there are viable alternatives to detect them well before V1. Visual inspection of the wing usually detects contamination and many aircraft automatically check for the take-off configuration to be set whenever the thrust increases beyond a pre-defined trigger level.
Increase in number of rejected take-offs: No system is perfect. It will detect some contaminated wing situations and save the day, but it will also cry wolf in cases where there is nothing to abort a take-off for. If the system has a false alert rate of one in ten thousand take-offs (which would be very good and expensive to design and certify) it would cause 15000 aborted take-offs (assuming the same numbers as above) for every crash it prevents (assuming a missed alert rate of 0).

Since lift increases with the square of air speed, it is difficult to detect lack of lift early on during the take-off run. At low speed there is relatively little lift to be expected and it will be in the noise of the measurement. Also the accuracy of the airspeed indicator is relatively low at low speeds, so the theoretical lift model will not give accurate results either. As a consequence the system will only be able to detect lack of lift at high speeds. At those higher speeds, the influence of bumps in the runway start to affect the measurements as well. It is easy to see that detecting lack of lift is no so straight forward. False alerts will be raised and they will be at raised at high speeds.
High speed rejected take-offs are risky.

Boeing studies indicate that approximately 75 percent of RTOs are
  initiated at speeds less than 80 kt and rarely result in an accident.
  About 2 percent occur at speeds in excess of 120 kt. The overruns and
  incidents that occur invariably stem from these high-speed events.

So effectively such a system will likely increase the number of accidents.

Icing primarily occurs in the air. Icing does not normally occur on the ground, except during conditions of freezing rain, which obviously the crew will be aware of because they must positively acknowledge weather conditions before getting a taxi clearance.
An aircraft will normally never take off if there is anything on the wings. The wings have to be absolutely clean before a pilot sets in motion a flight. Operating an aircraft with anything non-approved on the wing is a complete violation of FAA regulations and highly dangerous.
Apparently in some instances pilots have taken off even though conditions of freezing rain have loaded down a wing with ice--sometimes with fatal results. Obviously such actions are reckless in the extreme and indicate the crew has not only not done a walkaround or checklist, but not even bothered to look at the wing. As a pilot, I would consider doing something like this unthinkable, but apparently there are some pilots who have done this.
Although your idea of using wheel strut scales to avoid this is interesting and innovative, it may be difficult to put it into practice because the weight of the ice will be relatively small compared to the overall weight of the aircraft. Also, if the pilots are so reckless as to not visually check their wings during a freezing rain storm, doing spreadsheet-like calculations to trying to detect ice by weight are certainly not going to be on their agenda.

There have been incidents where airliners have crashed shortly after takeoff due to wing ice. I understand conditions have improved, but I have trouble believing your claim that it will never happen.

@raptortech97 Just to reiterate: aircraft NEVER take off with anything on the wing. Not even a Cessna will take off with so much as snow on the wing, nevermind ice. Icing does not occur on the ground. You have to fly in icing conditions for ice to build up. If you have a specific accident in mind, cite it.

How do you explain USAir 405, CEA 5210, Air Florida 90, and Air Ontario 1363?

Icing does not occur on the ground... yes it does. Read this accident report (pdf) of SAS 751 and learn. The wings have to be absolutely clean before a pilot will set in motion a flight.... Not every pilot, there are idiots.

@raptortech97 I stand corrected. Apparently you are right and multiple times ice loading has occurred on the ground. I find it absolutely incredible that a pilot would take off with ice on the wing, but apparently it happens. I have updated my answer. Thanks for the information.

Nice update. One correction: I didn't propose detecting ice by it's weight, I proposed detecting ice by the lower than expected lift in the takeoff roll. (Not to say that I still believe in my idea; your and DeltaLima's arguments are quite convincing.)


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How feasible is BAE Smart Skin?
I just came across this article on LinkedIn, and I have a few questions about it.
Some of BAe's claims are things such as:

Aircraft set to become more human as engineers develop smart skins which can detect injury
The revolutionary ‘smart skin’ concept will enable aircraft to continually monitor their health, reporting back on potential problems before they become significant. This would reduce the need for regular check-ups on the ground and parts could be replaced in a timely manner, increasing the efficiency of aircraft maintenance, the availability of the plane and improving safety.

In the past I have seen some claims of a similar nature (such as skin that adapts its shape to be more aerodynamic based on phase of flight).  What I am wondering is:

Is this really technically feasible?
Can such a skin really do what BAE claims?
Will this have any adverse effects on the aviation industry? (Usually people are so enamored with new technology and the good it can do, I am more curious if anyone has thought of the downside.)

broad claims over vague specs is standard for a PR department to get funding for their newest toys

Smart skins are at least 20 years old and, like fusion energy, just around the corner since then. The usual concept is to embed optical fibers in the structure and shine laser pulses through them. If the fiber is damaged, it will transmit less light, and by measuring the return time of a very short laser pulse, even the location of the damage can be detected. This concept requires fibers with the same break elongation as the load-carrying material, so they break just when a crack in the structure starts. To detect even small cracks, a lot of fibers must be evenly placed, which is only possible with fiber reinforced plastics. The effort to place a light source and a detector at each end of every fiber has so far prevented a practical application, at least to my knowledge.
Other techniques send clearly defined "pings" through the material and detect the propagation of the sound wave with a number of microphones. By comparing the measured signal with a reference signal, damage can be detected in metal structures as well. This technique needs some processing power, but is easily within the scope of modern microcontrollers. However, outside noise will interfere with the measurement, so it needs well defined conditions to be effective.
The downside would be more mass, investment and operator training. Generally, more advanced techniques for structural health checks have been steadily introduced in the last 80 years. Given the high cost of maintenance today, I expect that deployed damage detection technology will continue to advance, with a healthy time gap to what is possible in the laboratory. So there is some truth to those BAe claims, but I would hardly call it revolutionary.
Even more advanced are concepts of self-healing structures which contain capsules of a two-component resin. When the structure breaks, the capsules break as well and the freed resin helps to mend the crack.
If you ask me, the mass of those microcapsules would be better invested if it carries load right from the start, so the structure will tolerate higher loads and more load cycles. But I guess those research grants need to be spent somehow, and marketing departments need to write about revolutionary discoveries on a regular basis.

"like fusion energy, just around the corner since then" - LOVE that observation!

rather than sound, a standing EM field could also be used, changes in the field caused by breaks in the skin triggering sensors.

@jwenting: Good point, changes in conductivity and local capacitance give hints to damage, but sensors need to be fairly close to pick up the change. With acoustic excitation the sensors can be fewer and farther away.

@PeterKämpf possibly, though you want them in a reasonably dense grid to get an accurate location of the breach anyway, and acoustic sensors tend to be larger and more fragile than most.

Fusion has been "10 years form now" since the 1960s

@slebetman: Yes, it is older than smart skins, but the parallels were too obvious to refrain from the comparison.

If they ever get it to work on a production scale (and that's a big if) and economical to implement, it could mean aircraft detecting hairline fractures caused by metal fatigue themselves, rather than relying on regular X-ray scans of their structural components.

But that's for the future. For now the main application is the generation of funding for more research, which is the main application of most all research done in the last 20 years or more. Hence the mandatory phrase "more research is needed" at the end of every report coming out of every research department.
I once committed the mortal sin of not including that in a report, in fact I made it quite clear in my report that no further research into the topic was needed because the whole concept was bonkers and not economically viable (I was slightly more political in my wording but not all that much). It wasn't received kindly by the people who'd ordered the research, nor by its funders. It did get quite a few chuckles from my then colleagues outside of the specific department, there being little love lost between them and the team lead of the project I had been working on for the last 6 months as an intern.

So yes, it can in theory have very interesting implications for aircraft maintenance procedures, in practice though I seriously doubt we'll see any of it in more than a proof of concept form for a very long time.

I believe there is a prototype panel already in existence so the answer is yes it is possible...it's just a case of improving upon it and getting it onto a real plane
Also, you wouldnt want to use ant form of wiring (including optic cables) as that it big costs, and also would compromise the structure, and what happens if you break one of the bits?


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Calculation of temperature correction for altimeter
I try to calculate the correction of cold temperature for altimeter , i use for this the equation 24 of the Engineering Sciences Data Unit (ESDU) publication but it give me very high number .
if i take for example the given conditions
altitude of aircraft 1000 ft
0 ft for aerodrome altitude
t0 288 K
temperature deviation from the ISA = 259.9812
L0 = 0.001981
the result is 599777.4389 ft is too big , the expected result is 60 ft So where is mistakes ?

EDIT :
So i corrected the ISA dev according to what Ralph said but the result still incorrect i joint the step of calculation :

the expected result is 60 ft

259 degree temp dev from ISA is unreasonable by an order of magnitude. You may be mixing C and K units there. Please fix that & edit your question accordingly.

Infact 288degK at 0 ft altitude is = 15degC = ISA, so intended dev from ISA seems to be zero for purpose of the example question.

I agree, you are mixing temperature scales (K and C) and hence your incorrect result.

T aerodrome = 273K, T isa = 288K. so dT = 15K.  Applying the correct formula (see Namsters' answer below) gives 15/0.001981 * ln (1+ 1.981/288) = 51.90ft  (since dH aerodrome = 0).
The table from PANS OPS Doc 8168 uses an approximation which works for temps above -15C  (4 times the alt above the aerodrome in thousands of feet, times dT which equals 60).

Finaly i have found the answer the error is on all book that published the equation there is the true equation

What is the source of the original screenshot (i.e. what published the wrong equation)?

Yes the original equation is given in PANS OPS Doc 8168 Chapter 4 section 3.4

Can you specify what each variable is? I'm attempting to recreate this myself in excel. It would help greatly.


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What are the advantages and disadvantages of the MiG-29's horizontal stabilizers (not what do they do)?

The MiG-29's tail axes are located fairly close to the leading edge, and rotate along an axis oblique to the chord. What are the possible consequences to this arrangement (e.g. actuator torque, flutter potential)?

The horizontal surfaces can be shifted further aft, increasing their effectiveness and allowing to make them smaller.

But through the several evolutions it's gone through, right up to the MiG-35, the tail design hasn't changed, and the Russians are known for keeping things simple wherever possible, so there has to be an advantage or constraint that keeps it that way?

There is nothing too special about the MiG-29 stabilator.
The "slanted" (swept) axis of rotation is fairly common: as far as I remember, all MiGs that had a stabilator had this arrangement.
This has primarily structural advantages: it is easier to integrate the shaft (or axle) along the structural elements of the stabiliser, making it lighter. Also, the hinge moments are more consistent along the shaft. (For the straight shaft on a swept stabiliser, there will invariably be twisting forces that must be absorbed by the structure. Say, the root section may experience positive moment with respect to the shaft while the end section may have negative moment).
Also, as Charles already noted, a swept axis may allow to move the stabilator a bit further back (while keeping the same overall hinge moment), increasing its lever arm and thus efficiency. This is because the attachment point at the root can be closer to the leading edge. But this is only a gain when the actuator cannot be moved further back for some design reasons (like on MiG-29).
On the other hand, the leading edge may interfere with the fuselage when deflected, necessitating a "stump" at the root (which you can also see on most jet MiGs). At the same time, you need larger deflection in order to achieve the same aerodynamic effect (see also this answer).
The perception that the shaft is too close to the leading edge is a bit of an illusion. In fact, it is just a bit forward of the 1/4-chord line: exactly where it should be, as can be seen in these diagrams.

The further aft the stabilator is, the longer the moment arm, which means they can be smaller and still have the required pitch moment. But if the majority of the stabilator surface is behind the aircraft fuselage, (as in this case), then, even when the rotation axis is swept back, as it is on many Mig aircraft, the bulk of the aerodynamic surface can be behind the rotation axis, and if so the rotation axis will be forward of the fore-aft aerodynamically neutral point of the surface, (called the aerodynamic center (AC) - about 25% of the way back from the leading edge), which means the actuator that moves the stabilator must be larger (more powerful), to hold the stabilator in position, since the airloads when the stabilator is displaced from neutral will be higher.

The hinge line sweep allows the hinge line to stay near 25% of chord, so even with the rearwards shift the actuators need not be larger.

Peter, Are you saying that the Stabilator pivot axis is not normal to the fuselage reference line, that it is swept back at an angle? Wouldn't that cause the forward inboard edges of the stabilator to interfere with he side of the fuselage when it was deflected? And as close as the pivot is to the leading edge of the stabilator, ir would have to be swept back quite a bit to intersect with the 25% chord. Do you know what the axis sweep angle is?

No, I don't and only learned it from this question (and rotate along an axis oblique to the chord). You are correct about fuselage interference; this is why the moveable part sits on a stump and does not directly abut against the fuselage (see here for example).

Ahhh, I see that the inboard leading edge is aligned with the horizontally tapered fuselage extension (which I would assume holds the actuator and linkages), so that when the stabilator is deflected the forward tip, although it must move inboard, does not interfere with anything. Interesting design. Just looking at how far forward the pivot point is, I would think the swept back axis is still forward of the AC though.

I am editing my answer to reflect this.

This arrangement is for a better fulcrum (not pun intended here) in pitching. Advantage is that they hide the plum of exhaust heat at some angle of view form the enemie aircraft

The horizontal tails being thin and oriented more or less radially from the exhaust plume, I don't see much shielding of the exhaust & plume IR signatures except from a front aspect, which is pretty much the same for most all fighters.


text:
What happens when an airline pilot decides not to fly at the last minute?
What happens when a commercial airline pilot wants to remove himself from a flight a short time before takeoff (say an hour or less)? He obviously can't be forced to fly, and there may be very good reasons he shouldn't.
What is the penalty for the pilot?
What are the passengers told if it is something embarrassing, like a drunk pilot?
How long does it take to get a replacement pilot?
Surely the exact answers depend on the airline, but in general what happens? What regulations govern this situation?

Note that in theory there is almost certainly not a penalty, unless the pilot is an idiot: the pilot is actually obliged NOT to fly if he feels he is unfit through illness or similar

Similar, if not duplicate: What if pilot feels too tired before his flight?

In order to ensure safety of the flight the pilots are really protected and is rare having penalties (I can't however give you a more detailed answer). The drawback is that sometimes pilots use work-to-rule as a way to pressure airlines in negotiations (like salaries). But that's a different topic.

Not a dupe.  This is asking specifically about airlines.

There would be a great deal of variability on what happens depending on the airline, whether or not it was unionized, what country it was in, who the pilot was, and the specific situation of the flight involved.
The scenario of an hour or less is a truly rare occurrence. The system is set up to prevent such happenings. The last two carriers I worked for had a 2-hour showtime. If a pilot hadn't checked in or been picked up by that time, the search immediately started for a replacement.
The only occurrence of an approximate one hour replacement need that I'm personally aware of was when a captain failed a breathalyzer test at his 2-hour show time. Given the confusion of the moment, it was well less than 2 hours when they started the search for a replacement. There was no ready reserve, and no management pilots available that were current, so they had to start stealing captains from flights due to depart later. I was due to operate JFK to AMS around 2 hours after the JFK to TLV flight they needed a captain for, so they stole me off my flight, which meant they had to get someone else for that, etc.
There is good reason for a 2-hour showtime other than just making sure a pilot is there. There is work to be done, and that work has to be done by someone. In this case, a non-current management pilot did that work, including my cockpit flow. I went directly into cockpit, sat down, and called for the before start checklist.
There was in this instance a good reason to do what could be done to avoid taking a delay. Numbers of flights leave JFK for Europe and the Middle East in the evening. If you take a delay, you may well get a lower altitude than planned because someone ahead of you has grabbed it; everybody's going over the North Atlantic track system. If that happens, you need more fuel, which is more cost, etc.
What would happen to a pilot causing a one-hour replacement depends on so many things I won't even try to address that other than to say that it could range from no penalty whatsoever to immediate termination. In the case above, the captain was terminated, and since he was in his late 50s back when the age 60 retirement rule was in effect, it was the end of his airline career insofar as U.S. airlines were concerned.

In this case, a non-current management pilot did that work, including my cockpit flow. I went directly into cockpit, sat down, and called for the before start checklist. Did this cause any worry for our intrepid pilot since he hadn't personally verified all the checks, or is there simply enough trust in the system and the checklists that if 'they' say it's been done, you roll with it?

@Terry happy retirement! I hope you enjoy your post career flying as much as you did full-time :)

@FreeMan There was sufficient trust in the system, or rather should I say in the individual who did it even though he wasn't current. Plus, there was an experienced f.o., soon to upgrade, with whom the checklists had been run.

If a pilot removes themselves from a flight then the airline will attempt to find another pilot to replace them. Sometimes this can be done almost immediately if someone is available there at the airport (sometimes called "ready reserve" or "airport reserve"). Otherwise another reserve will have to be called from home. The amount of time given to a reserve pilot to appear at the airport varies by airline but is typically around two hours. This is normally called "short call reserve". If no one is available on short call then the flight will most likely be cancelled. There are other scenarios whereby a pilot can be removed from another flight to operate this one but this is less common.
A pilot that removes his/herself from duty may face company discipline depending on the circumstances.
There are really no relevant government regulations (in the United States, at least) other than those requiring a pilot to be fit for duty (and within legal duty and flight time restrictions).


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Can a vacuum cleaner create sufficient vacuum to operate the artificial horizon?
Inspired by this question about breaking the glass of instruments, I was wondering if a sufficient level of vacuum can be achieved by using a vacuum cleaner on the inlet, or simply sucking through a straw connected to the vacuum inlet, in case the artificial horizon's vacuum pump failed?

You go flying with a vacuum cleaner and a straw?  Wow. :)

you don't? You are violating FAR 112.3 section 6b: Emergency use of straws in flight

my airplane M20M has a standby vacuum pump

The answer is a qualified yes: It's theoretically possible, but wholly impractical to provide a pressure source to your gyros from within the cockpit, at least the way you're describing.

Air-Driven gyros require a relatively constant pressure differential somewhere between 4 and 6 inches of mercury to operate correctly (this can be "suction" or "pressure", but as vacuum/suction systems are more common let's stick with that term). We can split the difference and say we want to supply 5 inches of vacuum (which is usually right in the middle of the "green arc" for most vacuum gauges) - this is sufficient suction to keep the rotor spinning at an appropriate RPM so the instruments function as expected.
Because a constant vacuum is required we can kill off one of the options: You won't be able to suck air through a straw to do this -- you would be constantly over-speeding or under-speeding the gyro rotor as you produce either too much vacuum (inhaling) or not enough (when you have to let go of the straw to exhale).
The variable pressure would vary the rotor speed, and your instruments would be totally unreliable within a few breaths, defeating the purpose of the exercise.
A household vacuum can provide the necessary pressure differential (these fine vacuum-rating folks tell me that "An average vacuum will have a [suction] rating of around 80 inches of water", which Google tells me is around 5.9 inches of mercury. If you could hook the vacuum up to the aircraft's system downstream of the vacuum regulator (where the main vacuum pump hooks up) you could theoretically power your gyros normally.
There are some caveats to using a vacuum cleaner idea besides the obvious "How are you going to hook the vacuum up to the system?" question:

The vacuum cleaner specifications are presumably at or near sea level - they might not be able to provide adequate suction at higher altitudes.
Powering the vacuum cleaner in this scenario is left as an exercise for the reader (most aircraft with air-driven gyros don't have household AC power in the cockpit - you could install an inverter, but vacuums pull quite a lot of power, so you'd need a high-amperage circuit to supply it. The draw from the vacuum may exceed the capacity of the plane's electrical system, and to remedy that we're getting into complicated major alterations...)

There are other more practical alternatives to an engine-driven vacuum pump to consider if you're worried about the reliability of your vacuum source:

Precise Flight makes a standby vacuum system that ties into the engine intake.
For normally-aspirated engines this works well as long as the engine is operating at part throttle: The manifold pressure differential is sufficient that it can supply suction for your gyros.  The downside is that you can't guarantee a stable vacuum source: at full throttle there will probably not be sufficient suction to operate the gyros (particularly at altitude).
Pneumatic venturi tubes can be used to supply vacuum for aircraft in flight.
These are bolted on to the airframe and use the slipstream air moving through a venturi to create the necessary vacuum. In extremely slow flight these may also fail to provide adequate vacuum.
Electric standby vacuum pumps are a popular option as they offer you the ability to keep using your main vacuum instruments regardless of throttle position or airspeed. The primary drawbacks are weight, space (for the installation), and power to run the motor.
Electric gyro instruments are a popular option (though somewhat expensive): They provide a backup for the air-driven system using an independent power source.

Great Answer, but I'll dispute a few details...
The gyros have sufficient inertia that the unsteadiness of the vacuum caused by pausing to exhale would not likely cause the instruments to be unreliable. Listen to the gyros spin down after a flight to observe their inertia. The operation of the AI and HI instruments do not require a finely controlled, RPM of the gyro, so long as the RPM is adequate.  They provide a reference frame, not using metered precession for their primary function. The bigger problem is running out of self-generated suction before losing consciousness.

If you have a loose instrument, ^this^ is kind of fun to attempt.

Without taking data on performance of my Kirby at cabin pressures over FL200, I'm going to take an educated guess that powering a couple instruments is well within it's power capability.  The vacuum will be working with less-dense air at altitude, resulting in a higher rpm, but when the vacuum is loaded with a restricted flow, that RPM will likely drop significantly.  Remember the Kirby must produce a gauge pressure to operate the instruments, which it will still be able to do unless the air is so thin that it cannot spin at a high enough RPM to get the job done.

@2NinerRomeo Overspeed/Underspeed of the rotor in an attitude gyro can induce "interesting" overshoot/lag errors. Yes, the instrument will still function, but its accuracy may be degraded (and you have no way of verifying it in actual IMC). Re: a vacuum cleaner's performance at altitude, a vacuum is effectively a large fan moving a given volume of air. There are articles that cover this in more detail than I can.

(I would certainly be open to a vacuum cleaner powered gyro test - if someone wants to offer up a vacuum cleaner, an appropriate power source, and a sacrificial gyro I'd be happy to take the test rig flying & see how it behaves - it would be a cool experiment. I'm not taking the straw test up though, I'm not fond of having my passengers pass out :-D )


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How to anticipate the radius and rate of turn under specific conditions?
Given that an aircraft would normally start a turn from straight and level, how would one go about calculating the rate/radius of turn since there would be a delay before the aircraft can get to full bank etc. I am talking airliners.
Thank you.

You might find this answer helpful.

@Peter, Although the answer you reference was extremely informative, it is about roll rate and how it increases due to aileron deflection until reaching a steady stable rate. Isn't the OP's question more related to simply calculating how far the aircraft moves laterally during the delay while he/she is establishing the  desired bank angle?

@CharlesBretana. Yes, you are right. Yo need to add knowledge contained in this answer and maybe this answer, too.

@Peter, another topic related to roll rates, (but also not related to this OPs question) that is very interesting is Inertial Roll Coupling.

@CharlesBretana Yes, and you thought I wouldn't know?

Excellent topics, however I have had no luck in trying to incorporate them into my dilemma. I guess I am more after the distance travelled while establishing in a bank and then find a way to use that and add or subtract the radius of a turn formula. Will keep exploring and learning, but  if in the meanwhile anything else rings a bell all help would be appreciated.  Thank you.

@Peter, No I was not sure if you would know, it is a topic related to high performance aircraft like military fighters, and has become significant only relatively recently  (I remember one of the first aircraft losses attributed to this (F-16 at Nellis around late 80s), due to common practice of performing an aggressive, high rate of roll wing rock to acknowledge being shot down during training sorties.... But I knew that if not, you would be interested in it it..

@CharlesBretana Actually, the first airplane which experienced it (and helped to unveil the issue) was the X-3, all the way back in the early Fifties.

@Peter, Thanks! I did not know that. The accident I was referring to is here, if you're interested. Curiously, it does not mention inertial roll coupling, but I remember being briefed on this, and reading the accident report, which specifically mentioned it as being the result of rocking the wings at fairly high AOA after an energy dissipating defensive break turn.

@CharlesBretana: Yes, makes sense. Good to read that the pilot escaped unhurt. Now I guess the mods will scold us for having a discussion in the comments.

As it takes only a few seconds for an airliner to roll into a turn, the act of rolling in will not significantly affect the calculation of turn radius.
"Full bank", generally not exceeding 20-30 degrees with passengers (who wish to be comfortable), will an importantant factor.  Even more critical will be airspeed,  which for an airliner,  will be roughly in the range of 150 - 250 knots on approach to landing or departure.
The formula for Radius is:

R = V$^2$/(g x tangent bank angle)

Tangent bank angle is close to linear up to 30 degrees, so one may calculate (and plot) a "correction factor" based on a forward speed of 80 - 100 meters per second.  Notice the turn could also be "shaped" by reducing speed or increasing bank angle (within safe limits).
And since you have your radius of turn and velocity, rate of turn in degrees per second is derived as:

Rate = 360 degrees/[(2 × radius × Pi)/True Air Speed]second

An airliner at altitude flying at full tilt (TAS > 450 knots) will usually not need maneuvering of this type.

Thank you for your response. I have been using the formulas mentioned by you, however the delay in the bank (from 0 to 25 max) is causing the radius formula to not work and adding a time or distance based correction is not producing consistent results as the aircraft performance in turn seems to be heavily dependent on how wide or narrow the turn is. Thereby I was hoping for some formula to correct for this.  Thanks.

V3ER there is hope using one type of airliner at a given approach speed.  Keep in mind wind will figure greatly as well.  The pilots will have to adjust anyways to keep a standard ground track, which is why ground reference points, such as a church steeple, large building, lake, or sports field, can be very helpful in flying a pattern.

In order to calculate the radius, assuming an immediate change to 30° bank is a good first order assumption. Robert is right.
If you want to be more precise, you need to model the initial roll movement. Aileron deflection will happen within 1 second and rolling might maybe take another 2 seconds. Next, shortly before the desired roll angle is reached, ailerons are moved back to neutral. During this time the radius will shrink from infinite to the final value of the 30° bank turn. Due to the time it takes to move the ailerons, the plot of radius over time will have no sharp corners but will quickly and smoothly go from infinite to the final value where it will stay.
Again, assuming an immediate change to 30° bank does not incur a large mistake.


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How do variable bleed valves prevent surge?
All I know is that the valves open at low speed or when decelerating, and close at high speed or when accelerating. How do they prevent the compressor from stall or surge?

Stall is prevented by anticipating pressure variation and maintaining pressure in a safe area using the VBV, as explained in the answer to Why does the CF6/CFM56 Turbofan Fan Frame contain 12 circular holes between the primary and secondary flow? The stall/surge process is explained in If the intake of a running jet engine is blocked for some short duration what would be the sequence of events following it?

@mins With all respect to the answers linked in the comment (which are good answers!), the answers do not explain why the stall occurs at low spool speeds (the latter linked answer explains a rotating stall induced by an incident, but not why gas turbines are designed to blow off air), I hope the answer below sheds some light on that.

Valves open at low speed to prevent the blades to stall. At low spool speed, or a low power setting (low power setting => less fuel added to the cycle => less power in the turbine and as such less power available for the compressor), the volumetric flow through the fixed geometry compressor passage becomes too large (with respect to the design value, the compression is less at lower speed), blow-off of some of the air reduces the volumetric flow downstream of the bleed ports.
This can be explained with the so called velocity triangles/diagrams of the compressor:

The increase of the axial speed through the compressor (Uri increases) while the spool speed decreases (ωr decreases) causes the flow Vri angle (Uri - Vri) to become less steep and cause the flow to stall reducing the working of the compressor and blocking the flow passage; this is called surge. Blow-off of the air reduces the Uri flow velocity to prevent the compressor blades from stalling. Some compressors can change the geometry of the stator vanes to adjust for the change in inflow angle, this is referred to as Variable Stator Vanes, which extend the operating range. Bleed-off is the last resort to prevent surge.
This can be easily visualized by simulation of a gas turbine. The following example shows a gas turbine steady-state performance sweep (reduction of fuel) of a typical helicopter turboshaft engine plotted in the compressor characteristic. The dashed simulation does not incorporate a bleed schedule and crosses the surge line on the left (since this is a simulation with extrapolated map characteristics, this is mathematically possible, but not in real life, the compressor would stall and airflow would stagnate), the solid blue line represents the performance where a surge margin of 10 % is maintained by bleeding off compressor air (hence the parallel operating line region at low power).

The image shows the steady state performance/equilibrium line in the compressor characteristic, the transient working line would show a way different profile. The reason that bleed-off may be interesting for spooling up (more fuel added for a higher power setting) is that an instant increase in fuel will cause the amount of reaction product to increase causing the pressure inside the gas turbine to rise at the same spool speed (due to the inertia, the spool spooling up is relatively slow) which results in the working point to go to the surge line (following the constant spool speed line). Usually the amount of fuel is limited by the controller which gradually adds the fuel. If the working point gets to close to the surge line, bleeding off compressor air will prevent the compressor to surge.

What software did you use to generate that plot?  Is it open source, or otherwise available for use? Or if you didn't generate it, then what is the source of that image?  I've often wanted something to plot compressor maps to answer questions like this one but never had any publicly available software to do it.

@DanielK It's GSP, the Gas turbine Simulation Program, you can download a free copy at GSPteam.com.


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Where can I find full wing polar data to validate an aerodynamic code?
I am looking for polar data of a full wing to validate an aerodynamics code I an working on.
I am looking for the Cl, Cd polars (and Cmy) and the planform and airfoil geometry, I am also looking for the polars computed at various Mach numbers.
I looks through the Internet and read many AIAA papers but I never found all the elements I am looking for in one of them.
I heard about the ONERA M6, DLR-F4 and DPW reference wings but I never found a full study of one of those (with numerical data). If someone can provide me with such data I would be very happy.
To go one step further I am also looking for such kind of data for a straight wing.

Welcome to Aviation.SE! Can you clarify what you mean by polar data? Do you simply mean you wish to find the Cl, Cd & Cmy for a known wing geometry?

What I mean by polar data are the curves of Cl as a function of AoA and the curves of Cd and Cmy as a function of AoA or Cl for a given geometry and for given Mach and Reynolds numbers. I mean data because in many articles they provide with some curves but I would prefer having .dat or .txt files.

"Theory of Wing Sections" by Ira H Abbott and A. Von Doenhoff has extensive graphed and tabulated data for Cl and Cd vs alpha of a wide variety of wing sections.
Airfoiltools.com has also got a lot of the data you're looking for, but from a quick scan it doesnt appear to cite their sources. The data is readily available in tabulated format, however.
In either case, its not explicitly mentioned but I'd assume that the data provided is for wings of straight planform. I'd guess that you can find some kind of formula to account for the difference either in the Abbott book mentioned or elsewhere, possibly applying a variation of the blade element method.

Actually I am not looking for wing section polars but for full wing polars.

I need to have CFD data computed with a 3D solver as I want to validate my own 2D to 3D corrections


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Do airplanes or helicopters ever fly at night using only white navigation lights?
I've been trying to figure out if airplanes or helicopters ever fly at night with only white Nav Lights.
See this UAV video taken on July 12, 2015, 05:38 AM Pacific time in San Francisco, CA, USA.

Welcome to aviation.SE! What exactly is your question? Because this is a Q&A site, not a discussion forum, we generally avoid opinions and prefer questions that can have a clear answer. The [tour] may be helpful if you're new to the site.

I'm so sorry!  I've been trying to figure out if airplanes or helicopters ever fly at night with only white Nav Lights. That's the crux of my inquiry and in the course of google searching to answer my Q, I fell upon this website.  Again, very sorry if this is the wrong forum.  I'll take a look at the "tour."

Welcome to the site. Best to edit the question, and include the information from the comment.

Shaky camera work, limited resolution, in the dark. I assume you're intending to focus on the flickering lights to right of centre, which could be anything. Whichever answer you get to your posted question ('yes' or 'no') I don't see how that will provide any useful information.

There are no such things as white navigation lights - nav light, by definition, are red/green/white.
However, we're talking about filming lights at night. And the problem here is that the light source, no matter what colour, is a concentrated source of light in major contrast to the lack of light around it. And so the light will often 'burn in' on a camera and appear to be a lot of light, ie white, where the human eye will pick up the colours.


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What material and shape should be used for angle of attack sensors?
Does the material and shape of the vane for an angle of attack sensor have to be identical to the material and shape of the wing? What properties should I consider?

Look at an AOA sensor. Look at a wing. Are they the same shape? Why would it matter if they were made of different materials?

Why are you asking?

A wide variety of materials would suffice as an AOA sensor merely aligns itself with the wind as a weather vane and does not carry load.  Any non-warping reasonably strong material such as aluminum plate can be used in the design.
Since we are only measuring wind direction, look no further than old style delta shaped weather vanes, also found on turbine style wind mills.
Another quick AOA sensor could be a smoke trail, a ribbon, or a string. It just needs to follow the wind stream.
A symmetrical wing shape would work fine, a flat plate is easier to construct and is adequate
to the task.


text:
How is the impact force on the landing gear distributed in fighters?

Upon landing, what percentage of weight is distributed on the main and the nose landing gears of fighters?
Upon landing of a fighter aircraft, what would be the approximate time of transfer of the impact force on the landing gear?

Upon landing, the time to transfer impact force to the landing gear is “upon landing”, or effectively zero.  What makes you think there is a delay, or am I misinterpreting your question?

-1 because you spend zero effort on the title

Depends (as usual...)
On normal landings all the force is taken by the main gear - the nose gear is still in the air. Later on it only takes a small force compared to the impact of touchdown.
But: not knowing what aircraft and what kind of landing (normal controlled on land vs. the "crash" of carrier landings), the answer would not be able to be more specific.


text:
From which stages is the bleed air from a GE90?
I'm doing a university project on the GE90-115b engine and I'm having a hard time understanding this EASA type-certificate data sheet. In particular I can't figure out the air bleed extraction section (page 10 section 10). Is the stage number counted from the fan stage or from the LPC 1st stage?
Are there some specific reason for the choice of extraction air from "middle stages" instead of extracting it partially from low pressure stages and partially from high pressure ones?

The base engine (up -94B rating) has 10 stages HPC, the growth engine (up to -115B) has 9 (reference https://www.geaviation.com/commercial/engines/ge90-engine).
In both cases, the type certification is counting bleed starting from the first stage of the HPC (not the LPC).
The reference to "10th stage" bleed in the type certification is misleading.  There is no 10th stage bleed in either engine.  Rather it is "CDP" bleed.  "CDP" stands for "compressor discharge pressure", i.e. right after the last stage of the compressor.
So in the base engine, the last bleed is extracted immediately after the 10th stage, and on the growth engine it's extracted right after the 9th stage.
Below is a diagram showing the bleed air flow that may (hopefully) clarify.  The CDP bleed is in orange.

(image from this and this answer, original source)

The stage number is counted from the front of the compressor the bleed is tapped from, in this case I'm assuming its the HP compressor so 4th, 7th and 10th stage HP air.
Extraction locations depend really on what you want the air to do, turbine cooling, cabin conditioning, anti ice, start/surge/stall control etc etc, Whilst there are bleed point on some LP stages (CFM56 LP booster for example) its just dumped overboard as it doesn't contain enough energy to do any useful work.
 And you couldn't really mix LP and HP air because, like people fluids under pressure like to take the easiest route so HP would always overcome the LP and you'd just end up recycling the air.

This is what I thought too but, if I didn't misread the document, the HP compressor only has 9 stages.


text:
How does change in aircraft's weight equal fuel mass flow rate multiplied by 'g'?
Can someone help me understand how does
$$\frac{dW}{dt} = -\dot{m}_f \cdot g ,$$
where $\dot{m}_f$ is fuel mass flow rate.
This is the first equation laid down in the Breguet range equation derivation.
Here's where I encountered it. Alternative accessible source (link):

In the SI system the weight is measured in Newtons [N = kg*m/s^2], while the mass is measured in kilograms [kg].
To convert kilograms in Newtons, i.e. a mass measurement in a weight, you multiply by the acceleration of gravity g.
In this case you're converting a change in mass to a change in weight, the conversion is the same, but both sides have an additional time component in the denominator due to the derivative.
Given your comment, it seems you're confused by the good old mass-vs-weight thing. Let's have Wikipedia:

In common usage, the mass of an object is often referred to as its weight, though these are in fact different concepts and quantities. In scientific contexts, mass is the amount of "matter" in an object (though "matter" may be difficult to define), whereas weight is the force exerted on an object by gravity. In other words, an object with a mass of 1.0 kilogram weighs approximately 9.81 newtons on the surface of the Earth, which is its mass multiplied by the gravitational field strength. The object's weight is less on Mars, where gravity is weaker, and more on Saturn, and very small in space when far from any significant source of gravity, but it always has the same mass.

You have explained the dimensionality of the components, all right. But I am trying to understand how does mass flow rate, which from my thermodynamics class equates $\rho Av$, multiplied by gravity equates to $dW/dt$! Unless $m_f$ means something completely different here.

@hegemon8 yeah, mass flow rate can also be represented as $\rho A v$, but it is still $\dot m$. And the relationship between $\dot m$ and $\dot W$ is a simple factor of $g$. Mass is one thing, Weight is a measure of the force felt by the mass in a gravitational field.

@hegemon8, density $\rho$ is mass per volume ([kg/m³]), $A$ is area [m²] and velocity is distance per time ([m/s]), so multiplying them together you get mass per time ([kg/s]), the mass flow rate.

@Federico Oh, yes. Quite silly of me actually. I was extrapolating things where none's necessary. Thanks.

The equation you've posted is saying that planes get lighter because they burn fuel.  When you mathematically model aircraft, that's often the only significant weight difference, and understanding what the aircraft weighs is important for knowing how much lift the aircraft needs to produce, which changes the drag, and so on...
Treat that equation as a statement that FOR THAT MATHEMATICAL MODEL the ONLY change in the aircraft's weight is caused by it using fuel.
If you were modeling combat aircraft that will be expending weapons, or transport aircraft that air-drop cargo (like a skydiving aircraft), that equation might change to include terms for those payload weights as well.

Sincerely I don't see how this addresses OP's question

@Federico you've already seen the comment on your answer.  It's clear the OP doesn't understand why the weight change equals the fuel mass flow.  This is why.

yes, they're confused by the transformation of a delta mass into a delta weight. I don't see how it helps them (or how it provides an explanation) talking about payloads and so on. But I gues we'll see if/when they comment

I talk about the payloads because a student taking a course including Breguet Range equations is likely to be asked about aircraft range in situations that involve more than just fuel.  That's the way it worked in my aerospace undergrad.